1. Field of the Invention
This invention relates to the treatment of seizure disorders and, and more particularly relates to techniques for preventing epileptic seizures.
2. Description of Related Art
Epilepsy is a condition characterized by recurrent seizures which are the outward manifestation of excessive and/or hyper-synchronous abnormal electrical activity of neurons in the cerebral cortex of the brain. A seizure often occurs when the electrical activity of the brain becomes more xe2x80x9csynchronizedxe2x80x9d as would be the case when the person is in a drowsy state.
A seizure patient may suffer from any combination of different types of seizures. Grand mal seizures are the most common form of epilepsy and are characterized by convulsions with tonic-clonic contractions of the muscles. Absence seizures (previously referred to as xe2x80x9cpetit malxe2x80x9d) are characterized by a brief and sudden loss of consciousness. The psychomotor form of seizures is characterized by a clouding of consciousness for one or two minutes. A complex partial seizure is characterized by a complete loss of consciousness. The type of seizure experienced is typically dependent upon the function of the portion of the cerebral cortex where hypersynchronous activity is occurring. Many types of seizures generally involve the entire brain, while certain types, such as partial seizures, begin in one part of the brain and may remain local.
Regardless of the type of epilepsy, seizures significantly limit the autonomy of the patient. When hit with a seizure attack, the patient typically loses some level of control of his/her body. In most cases, seizures occur without prior warning to the patient. As a result, epileptic seizures pose a serious safety hazard to the patient as others surrounding the patient. For example, a patient hit with a sudden seizure attack while he/she is driving a car may endanger his/her own safety as well as the safety of others. Seizure patients are also exposed to a risk of bodily harm when operating machinery and even in daily activities such as crossing a street or going down stairs.
Researchers have developed a number of techniques for treating seizure disorders and its symptoms. For example, research has shown that inhibiting (namely, reducing the excitation of neurons) the substantia nigra in the brain increases the threshold for seizure occurrence. Researchers have also found that increasing the activity of neurons in the external Globus Pallidum (GPe) increases inhibition of neurons in the subthalamic nucleus which in turn inhibits neural activity in the substantia nigra. Neurosurgeons have also been able to diminish the symptoms of many neural disorders by lesioning certain brain areas, examples being lesioning the ventral lateral portion of the internal Globus Pallidus and the Vim Thalamus for treating movement disorders. Alternatively, it has been demonstrated that open-loop Deep Brain Stimulation (DBS) at high frequencies (100 Hz or higher) of certain brain structures can alleviate, diminish, or completely stop symptoms of tremor, rigidity, akinesia or hemiballism much like creating a lesion. Electrical stimulation of the nervous system has also been used to suppress seizures. Finally, infusion of certain drugs into a region of the brain can affect the excitability of the neurons at the site of infusion as disclosed in U.S. Pat. No. 5,713,923 (Rise et al.) assigned to Medtronic, Inc.
Under another approach, researchers have devised algorithms to detect the onset of a seizure. Qu and Gotman reported a system that recognizes patterns of electrical activity similar to a template developed from recording an actual seizure. See H. Qu and J. Gotman, xe2x80x9cA Seizure Warning System for Long-term Epilepsy Monitoringxe2x80x9d, Neurology, 1995;45:2250-2254. Similarly, Osario et. al. have reported an algorithm applied to signals recorded from intracranial electrodes capable of 100% seizure detection rate with 0% false negatives and minimal false positives. See I. Osario, M. Frei, D. Lerner, S. Wilkinson, xe2x80x9cA Method for Accurate Automated Real-time Seizure Detectionxe2x80x9d, Epilepsia, Vol. 36, Suppl. 4, 1995. In each of these techniques for recognizing the onset of a seizure, the developers employ two processes. The first process is to extract certain features from the signals representing the electrical activity of the brain. Examples of the signal features include the signal power or the frequency spectrum of the signals. The second process is to recognize a pattern or set of values for those features which characterize a brain state that will reliably lead to a seizure.
Others have studied the effects of electrically stimulating the vagus nerve as a means of xe2x80x9cdesynchronizingxe2x80x9d the electrical activity of the brain. It has been observed that stimulation of the vagus nerve with certain parameters caused de-synchronization of the brain""s electrical activity in animal models. These concepts were disclosed by Zabara in U.S. Pat. Nos. 4,867,164 and 5,025,807. De-synchronization can be thought of as xe2x80x9calertingxe2x80x9d phenomena since it reflects active mental activity.
An alternative way to xe2x80x9calertxe2x80x9d someone is to activate the sense of smell especially by use of an astringent. The most common example of this phenomena is seen when an athlete is knocked unconscious and the trainer uses an ammonia capsule to stimulate the person to regain consciousness. When, the person breaks the ammonia capsule under the athletes nose is stimulates the olfactory nerve and certain branches of the trigeminal nerve. The trigeminal nerve is a cranial nerve which connects with and provides input into the brainstem. Zabara teaches that stimulation of the trigeminal nerve will inhibit the occurance of seizures (U.S. Pat. No. 5,540,734). The olfactory nerve ultimately provides input into the entorhinal cortex. The entorhinal cortex is located at the tip of the temporal lobe surrounding the amygdala, a structure implicated in temporal lobe epilepsy.
The present invention is directed to improve on existing methods of desynchronizing the nervous system and thereby decrease the likelihood of having seizures by persons with epilepsy.
As explained in more detail below, the present invention overcomes the above-noted and other shortcomings of prior techniques for warning of epileptic seizures.
A preferred form of the invention consists of a sensing portion capable of detecting the onset of a seizure, a signal processing portion, and a therapy delivery portion. The sensing portion may be an electrical sensor, chemical sensor, and/or a sensor for sensing physiological changes. The particular structure and parameter to measure may be selected from any known techniques which provide indication of the possible onset of a seizure. The signal processing portion processes and analyzes the sensed signal using an algorithm for recognizing a pattern scheme indicative of the onset of a seizure. If a pattern indicative of the onset of a seizure is recognized, the therapy delivery portion is triggered. The therapy delivery portion is preferably a stimulation electrode which delivers sensory stimulation to the olfactory sensory system of the patient thereby decreasing the likelihood that a seizure will occur.
Under another embodiment, the invention includes a therapy delivery portion. Under this embodiment, the therapy delivery portion provides sensory stimulation to the olfactory sensory system of the patient in a continuous or periodic manner to thereby decrease the likelihood that a seizure will occur.
By using the foregoing techniques, seizure disorders, including epilepsy, can be treated and seizures can be alleviated or prevented using olfactory sensory stimulation. Examples of the more important features of this invention have been broadly outlined above in order that the detailed description that follows may be better understood and so that contributions which this invention provides to the art may be better appreciated. There are, of course, additional features of the invention which will be described herein and which will be included within the subject matter of the claims appended hereto.